The present invention relates to infrared sensor systems. In particular, the present invention relates to hybrid infrared system focal planes.
Previous designs of cryogenically cooled infrared focal planes can be characterized by a limited number of photodetector elements, an absence of preamplifiers or other signal processing elements, and a large complement of signal leads. Preamplification and other signal processing is carried out external to the Dewar. The complexity of the focal planes has been limited by the number of signal leads which can be routed from inside the Dewar, through vacuum seals, to the associated electronics outside of the Dewar.
Recent developments in semiconductor technology have led to the feasibility of more complex infrared system focal planes, with more sensitivity, higher resolution, higher data rate and greater reliability. These developments include advances in microelectronics, especially in charge transfer devices, MOS technology, and large scale integration.
The advent of charge transfer devices and their supporting technology introduces several major benefits. First, it is now possible to consider carrying out a variety of signal processing tasks in situ on or near the focal plane. Second, the multiplexing capability of charge transfer device permits a dramatic reduction in the number of leads leaving the focal plane.
The integration of infrared detector and signal processors on the focal plane, therefore, reduces the number of electrical feedthroughs and decreases the system complexity. Higher system performance becomes possible, along with considerable reduction in overall cost.
The development of hybrid focal planes containing both infrared detectors and associated signal processing, however, presents several technical challenges. First, the typical infrared detector materials are mercury cadmium telluride, lead tin telluride, lead selenide telluride, and indium antimonide. The signal processing portions of the hybrid focal plane, however, will typically be silicon because the silicon technology is far more advanced than those of the typical infrared detector materials. In addition, the large bandgap of silicon provides certain advantages over the narrower bandgaps of the typical infrared detector materials. The design of a hybrid focal plane, therefore, must accommodate infrared detectors and signal processors which are formed from different semiconductor materials.
Second, it is highly desirable to provide very high packing density of photodetectors on the focal plane. This complicates the interconnections of the photodetectors to the associated signal processing circuitry.
Third, since the photodetectors and the signal processing circuitry will be processed at different times, it is important that the processing of the infrared detectors does not adversely affect previously formed solid state signal processing circuitry, or vice versa.